You should create your own file. There's a sample one you can see, link is on the home page, it's getting a bit old now and I need to update it.
You place it in the ".napshare" folder where the other config files are.
It's basicly just a text file with a URL for each gwebcache per line, you could probably get connected to the network with only one listed, but I would put in 10 or more.
I will have to get to the code and get more fancy on this, but for now this works.
You can also search google with the keyword "gwebcache" to find them.